Hollow fiber carbon membrane and method for manufacturing hollow fiber carbon membrane

Abstract

The present invention relates to a method for manufacturing a hollow fiber carbon membrane, the method comprising a step (a) for preparing a carbon-membrane-forming stock solution and molding hollow fibers through a spinning method for subjecting the carbon-membrane-forming stock solution to non-solvent-induced separation using a double annular nozzle, a step (b) for winding the molded hollow fibers onto the outer periphery of a bobbin having a polygonal outer periphery, a step (c) for heating the wound hollow fibers while rotating the bobbin to perform a crosslinking treatment, a step (d) for raising the temperature of the post-crosslinking-treatment hollow fibers from a prescribed temperature and heating and infusibilizing the hollow fibers, and a step (e) for subjecting the hollow fibers subjected to the infusibilization treatment to a carbonization treatment, the carbon-membrane-forming stock solution containing polyphenylene oxide in an amount of 15-40 mass%, sulfur in an amount of 7-15 mass% with respect to the polyphenylene oxide, and a solvent capable of dissolving the aforementioned components.

Description

Hollow fiber carbon membrane and method for producing hollow fiber carbon membrane

[0001] The present invention relates to a hollow fiber carbon membrane and a method for producing the hollow fiber carbon membrane.

[0002] Various organic and inorganic membranes have been studied for use as separation membranes for gases and the like. Organic membranes made of polysulfone, cellulose acetate, etc. have the advantages of good formability and low cost, but they have poor solvent resistance and heat resistance. On the other hand, inorganic membranes have the advantages of excellent solvent resistance and heat resistance, but are difficult to form and expensive. Therefore, hollow fiber carbon membranes, which are inexpensive and have excellent formability, solvent resistance, and heat resistance, have been attracting attention in recent years.

[0003] Hollow fiber carbon membranes have pores of a size that allows gas separation, and they exhibit superior gas separation performance compared to various inorganic membranes. They also have heat and chemical resistance that organic membranes cannot meet, making them highly promising for practical use. Furthermore, hollow fiber carbon membranes have excellent pressure resistance and occupy a large membrane area per unit volume, making it possible to fabricate compact separation membrane modules.

[0004] Proposed hollow fiber carbon membranes include those using a sulfonated polyphenylene oxide resin as a raw material (Patent Documents 1 and 2), those using an aromatic polyimide (Patent Document 3), etc. Also, in order to produce a hollow fiber carbon membrane with excellent cost performance, a method for producing a hollow fiber carbon membrane is known in which hollow fibers are spun using polyphenylene oxide, a general-purpose and inexpensive raw material, as a raw material, and the hollow fiber is then subjected to two heating steps: an infusible treatment step and a carbonization treatment step (Patent Document 4).

[0005] In the first heating step of the two-stage heating process disclosed in Patent Document 4, that is, a step of crosslinking in air at 200 to 240°C and then heating at 250 to 350°C to make the hollow fiber membrane infusible, it is necessary to insert the hollow fiber membrane into a resin tube made of perfluoroalkoxyalkane resin to prevent adhesion between the hollow fibers, that is, to ensure that the hollow fibers are not in contact with each other. If the infusible treatment is completed while the hollow fibers are still infusible, they will be molded in an inseparable state, resulting in molding defects.

[0006] Furthermore, to prevent the hollow fibers from adhering to the inside of the resin tube, the resin tube is made of a heat-resistant, non-adhesive fluororesin such as perfluoroalkoxyalkane, but perfluoroalkoxyalkane resin is more expensive than general resins, and thousands of resin tubes are required per module, which increases the cost of components. Furthermore, the work of inserting the hollow fibers into the resin tube is done manually, one by one, and requires careful handling, so the manufacturing cost of the module increases in proportion to the number of fibers to be processed.

[0007] Therefore, although conventional methods for producing hollow fiber carbon membranes can produce hollow fiber carbon membranes with excellent separation properties, they increase the costs of components and production, and therefore there is a need for the development of a new production method that enables mass production of hollow fiber carbon membranes at low cost.

[0008] JP 2009-34614 A JP 2013-94744 A JP 2000-185212 A WO 2016 / 093357

[0009] The present invention provides a method for producing hollow fiber carbon membranes that enables mass production of hollow fiber carbon membranes at low cost, and a hollow fiber carbon membrane obtained by the method.

[0010] A method for producing a hollow fiber carbon membrane according to an embodiment of the present invention includes: a step (a) of preparing a carbon membrane dope solution, and forming a hollow fiber from the carbon membrane dope solution using a double annular nozzle by a spinning method based on a non-solvent-induced separation method; a step (b) of winding the formed hollow fiber around a bobbin having a polygonal outer periphery; a step (c) of heating the wound hollow fiber in air at 200°C to 220°C while rotating the bobbin to perform a crosslinking treatment; a step (d) of heating the crosslinked hollow fiber from 200°C to 220°C and then to 250°C to 350°C to perform an infusibilization treatment; and a step (e) of carbonizing the infusibilized hollow fiber, wherein the carbon membrane dope solution contains polyphenylene oxide in an amount to give a concentration of 15 to 40% by mass, sulfur in an amount to give a ratio of 7 to 15% by mass relative to the polyphenylene oxide, and a solvent capable of dissolving them.

[0011] In one embodiment of the present invention, the polygon is a quadrilateral.

[0012] In one embodiment of the present invention, in the step (b), the hollow fiber is wound up in a linear shape.

[0013] A hollow fiber carbon membrane according to an embodiment of the present invention contains sulfur-crosslinked polyphenylene oxide and has a tensile strength of 30 MPa or more.

[0014] In one embodiment of the present invention, the hollow fiber carbon membrane is a hollow fiber carbon membrane for a gas separation module.

[0015] According to the present invention, it is possible to provide a method for producing hollow fiber carbon membranes that enables mass production of hollow fiber carbon membranes at low cost, and hollow fiber carbon membranes obtained by the production method.

[0016] Fig. 1 shows the results of DTA measurements when varying the concentration of sulfur is added to polyphenylene oxide, which is a raw material for hollow fiber carbon membranes. Fig. 2 is a schematic diagram showing one embodiment of step (b) in the method for producing a hollow fiber carbon membrane of the present invention.

[0017] Hereinafter, a method for producing a hollow fiber carbon membrane according to an embodiment of the present invention and a hollow fiber carbon membrane produced by the method will be described in detail.

[0018] [Method for Producing Hollow Fiber Carbon Membranes] The method for producing hollow fiber carbon membranes according to the present invention includes the steps of: (a) preparing a carbon membrane dope solution and forming a hollow fiber; (b) winding the formed hollow fiber around a bobbin having a polygonal periphery; (c) crosslinking the wound hollow fiber while rotating the bobbin; (d) infusibilizing the crosslinked hollow fiber; and (e) carbonizing the infusibilized hollow fiber. The carbon membrane dope solution used in step (a) contains polyphenylene oxide in an amount that results in a concentration of 15 to 40 mass %, sulfur in an amount that results in a ratio of 7 to 15 mass % relative to the polyphenylene oxide, and a solvent capable of dissolving them. By using a carbon membrane dope solution containing polyphenylene oxide with a high amount of sulfur added, the crosslinking reaction can be initiated and progressed more quickly, thereby reducing adhesion between hollow fibers. Furthermore, by using a predetermined hollow fiber winding bobbin, hollow fibers can be wound at regular intervals, and by performing crosslinking and infusibilization treatments in this state, straight hollow fibers can be stably obtained without the need for resin tubes to prevent adhesion between the hollow fibers. As a result, it becomes possible to process a large number of hollow fibers, in units of 1,000, at once, rather than processing each hollow fiber individually, thereby achieving significant reductions in material costs and production costs.

[0019] <Step (a)> In step (a) as a spinning step, a carbon membrane forming solution is prepared, and the carbon membrane forming solution is spun into hollow fibers using a double annular nozzle by a non-solvent-induced separation method. The carbon membrane forming solution contains polyphenylene oxide in an amount that results in a concentration of 15 to 40 mass %, sulfur in an amount that results in a ratio of 7 to 15 mass % relative to the polyphenylene oxide, and a solvent that can dissolve these. Here, the double annular nozzle has a double-pipe annular structure including an inner tube and an outer tube that is spaced apart from the inner tube and covers the inner tube, and has a structure that allows different materials to be simultaneously extruded from the inner tube and the outer tube. The prepared membrane-forming solution is extruded into a coagulation bath through the outer tube of a hollow fiber spinning nozzle with a double-tube ring structure, either directly or via idle running, by a spinning method using a non-solvent-induced separation method such as wet spinning or dry-wet spinning. A hollow fiber is then formed by simultaneously extruding the membrane-forming solution solvent, a polymer-insoluble solvent, or a mixture thereof, as a core liquid through the inner tube of the hollow fiber spinning nozzle. In this process, a hollow fiber carbon membrane having a predetermined membrane outer diameter can be obtained by appropriately adjusting the diameter of the outer tube of the hollow fiber spinning nozzle and the winding speed of the hollow fiber around a bobbin (described below). The formed hollow fiber may be further washed with water, if necessary.

[0020] Next, the hollow fiber spun as described above is wound onto a cylindrical bobbin and held there. The outer diameter of the bobbin is preferably 0.5 to 2.0 m, more preferably 0.7 to 1.2 m, and the winding speed of the hollow fiber around the bobbin is preferably 10 to 60 m / min, more preferably 20 to 40 m / min. The total length of the hollow fiber wound onto the bobbin is preferably 100 to 8,000 m, more preferably 2,000 to 4,000 m. The hollow fiber wound onto the cylindrical bobbin in this manner may be immediately subjected to the subsequent step (b), or the formed hollow fiber may be stored in water for a certain period of time.

[0021] The polyphenylene oxide is preferably a polyphenylene oxide-based polymer, more preferably polyphenylene oxide or a derivative in which 1 to 4 hydrogen atoms constituting the aromatic ring of polyphenylene oxide are directly substituted with functional groups selected from the group consisting of halogen atoms, sulfone groups, carboxyl groups, lower alkyl groups, tri(lower alkyl)silyl groups and diarylphosphino groups, or -CH ２ It is a derivative in which these atoms or functional groups are substituted via a -. The lower alkyl is preferably an alkyl having 1 to 5 carbon atoms.

[0022] As such polyphenylene oxide, for example, commercially available products such as PPO646 (manufactured by SABIC), PX100F, and PX100L (all manufactured by Mitsubishi Engineering-Plastics Corporation) can be used as they are. In the carbon membrane forming solution, polyphenylene oxide is used at a concentration of 15 to 40 mass %, preferably 20 to 35 mass %. If the polyphenylene oxide concentration is higher than 40 mass %, the membrane forming solution will separate, making spinning impossible. On the other hand, if the concentration is lower than 15 mass %, the carbon membrane will become brittle during firing, and a good carbon membrane may not be obtained.

[0023] The carbon membrane forming solution further contains sulfur in an amount of 7 to 15 mass %, preferably 9 to 12 mass %, relative to the polyphenylene oxide. This sulfur content range allows the crosslinking reaction to begin at temperatures around 200 to 210°C, and the crosslinking reaction proceeds rapidly, reducing adhesion between hollow fibers during crosslinking treatment of the hollow fibers. Furthermore, an increase in the kinetic viscosity of the carbon membrane forming solution reduces the fluidity of the carbon membrane forming solution, improving the shape retention of the hollow fibers and improving the formability of the carbon membrane. Furthermore, crosslinking a larger amount of sulfur to polyphenylene oxide allows for the production of hollow fiber carbon membranes with superior strength. Furthermore, sulfur is added to the carbon membrane forming solution in an amount of 1.5 to 4.0 mass %, preferably 2.0 to 3.5 mass %, relative to the carbon membrane forming solution.

[0024] Figure 1 shows the results of DTA measurements (differential thermal analysis, from 200°C to 300°C) when the amount of sulfur added to polyphenylene oxide (based on 100 parts by mass) is increased. As shown in Figure 1, as the amount of sulfur increases, the exothermic peak of crosslinking appears on the lower temperature side, and it can be seen that the crosslinking reaction starts at around 200 to 210°C.

[0025] The carbon membrane forming solution may further contain other crosslinking agents, such as organic peroxide-based crosslinking agents, including dialkyl-based peroxides such as di(2-tert-butylperoxyisopropyl)benzene, dicumyl peroxide, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane and 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane-3, diacyl-based peroxides such as diisobutyryl peroxide, phenolic resin-based crosslinking agents, and quinone dioxime-based crosslinking agents, which have a crosslinking effect together with sulfur.

[0026] The carbon membrane forming solution is prepared by dissolving polyphenylene oxide, sulfur, and optionally other crosslinking agents in a solvent capable of dissolving these components. The dissolution is carried out by first dissolving sulfur in a solvent, and then dissolving polyphenylene oxide in the solvent. Examples of such a solvent include tetrahydrofuran, N,N-dimethylacetamide, and N-methyl-2-pyrrolidone. Preferably, aprotic polar solvents such as N,N-dimethylacetamide and N-methyl-2-pyrrolidone are used. These solvents may be used alone or in combination of two or more.

[0027] To prevent the carbon membrane forming solution from cooling and causing phase separation, the solution may be heated and maintained using heaters or the like in the hollow fiber spinning nozzle and transport piping. The temperature for maintaining the temperature is preferably 80 to 160°C, more preferably 110 to 140°C. The core liquid and coagulation bath are made of a solvent that is insoluble in polyphenylene oxide, such as water, ethylene glycol, or a mixture thereof. The temperatures of the core liquid and coagulation bath are preferably −20 to 60°C, more preferably 0 to 30°C.

[0028] <Step (b)> Next, the formed hollow fiber is wound onto the outer periphery of a bobbin having a polygonal outer periphery. Here, the "outer periphery of the bobbin" refers to the periphery of the side surface of the bobbin (cross section perpendicular to the rotation axis of the bobbin) that holds the wound hollow fiber. If the bobbin has a lattice shape, the bobbin has a shape formed by lattice points when viewed in a cross section perpendicular to its rotation axis. The formed hollow fiber is then fed from the cylindrical bobbin and wound onto the outer periphery of the bobbin having a polygonal outer periphery. The shape of the outer periphery of the bobbin is not particularly limited as long as it is polygonal, and examples include a triangle, a rectangle, a pentagon, a hexagon, and other n-gons (n ​​is an integer of 7 or more). However, from the viewpoints of excellent bobbin winding performance, excellent linearity of the hollow fiber shape after heat treatment, and ease of storage when installing the bobbin in a heating device, the shape (polygon) of the outer periphery of the bobbin is preferably quadrangular. The outer periphery of the bobbin may be either a regular polygon or a polygon with different interior angles, but a regular polygon is preferred because it provides excellent linearity to the hollow fiber shape.

[0029] Furthermore, since the wound hollow fibers can be held in a straight line, the hollow fibers can be prevented from bending when they are dried while wound around a cylindrical bobbin. The resulting hollow fiber carbon membrane is a brittle material, which is fragile like a glass tube. When fabricating a prototype module consisting of a bundle of 100 to 1,000 hollow fiber carbon membranes, bending the hollow fibers can easily break them during handling and can reduce the number of fibers packed per unit volume. Therefore, winding the hollow fibers in a straight line can improve the formability of the hollow fiber carbon membrane.

[0030] FIG. 2 illustrates an example of a bobbin having a rectangular outer periphery. The bobbin 2 in FIG. 2 has a lattice pattern, and while rotating in the direction A, the hollow fiber 1 can be wound around the outer periphery 4. The outer periphery 4 has a rectangular shape formed by four lattice points originating from corners 3 in a cross section perpendicular to the rotation axis of the bobbin 2. Thus, the hollow fiber 1 is wound linearly around the bobbin 2, excluding the corners 3 on the outer periphery. Therefore, as the bobbin 2 rotates, the core liquid (typically composed mostly of water) remaining inside the hollow fiber 1 easily moves due to gravity inside the hollow fiber 1, permeating and penetrating the hollow fiber 1 and evaporating from the surface of the hollow fiber 1. Therefore, there is no need for additional processing or steps to remove the core liquid from the hollow fiber 1. This allows the hollow fiber 1 to be dried efficiently and in a short time, thereby improving the production capacity of the resulting hollow fiber carbon membrane. Furthermore, since the hollow fiber 1 maintains a linear shape along the outer periphery of the bobbin 2 after drying, the formability of the hollow fiber carbon membrane can be improved.

[0031] The length of the hollow fiber 1 when the hollow fiber 1 is wound around the outer periphery of the bobbin 2 in FIG. 2 (i.e., the circumferential length of the bobbin 2) is preferably 1 to 4 m, more preferably 2 to 4 m. The winding speed of the hollow fiber 1 around the bobbin 2 in FIG. 2 is preferably 2 to 40 m / min, more preferably 12 to 24 m / min. If one turn of the hollow fiber 1 is defined as one turn of the hollow fiber 1 wound around the outer periphery of the bobbin 2 in FIG. 2, the hollow fiber 1 is preferably wound around the bobbin 2 by 400 to 1,200 turns, more preferably 600 to 1,000 turns. When winding the hollow fiber 1 around the bobbin 2 in FIG. 2, a coil-shaped groove can be provided so that the hollow fiber 1 for one turn is spaced apart from each other by preferably 0.5 to 8 mm, more preferably 1 to 2 mm. When winding the hollow fiber 1 around the bobbin 2, ventilation may be used to accelerate drying of the hollow fiber 1. The air flow rate at this time is preferably 5 to 100 cm / sec, more preferably 30 to 80 cm / sec, in terms of linear velocity.

[0032] The material of the bobbin is not particularly limited as long as it has heat resistance of 300° C. or higher, and for example, bobbins made of metal materials such as stainless steel, carbon steel, etc. Among these, lightweight metal materials such as aluminum steel, which have a small rotational load and are easy to transport, are preferred.

[0033] <Step (c)> Next, the hollow fiber wound in step (b) is crosslinked while rotating the bobbin. The crosslinking treatment is carried out in air by heating to 200°C to 220°C at a temperature increase rate of 0.1 to 4°C / min, preferably 0.2 to 2°C / min. In step (a), when preparing the carbon membrane forming solution, adding 7 to 13 mass% of sulfur relative to the polyphenylene oxide allows the crosslinking reaction to proceed even in a low-temperature environment of 200°C. After the heating temperature reaches 200°C to 220°C, the heating temperature is maintained at 220°C for 0.5 to 8 hours, preferably 1 to 4 hours, to achieve the crosslinking reaction.

[0034] <Step (d)> Next, the crosslinked hollow fibers are subjected to an infusible treatment. The infusible treatment is carried out by heating the crosslinked hollow fibers from 200°C to 220°C in air at a temperature increase rate of 0.1 to 4°C / min, preferably 0.2 to 2°C / min, to 250°C to 350°C, preferably 280°C. In the infusible treatment, the crosslinked hollow fibers are heated at a temperature lower than the temperature in the carbonization treatment step described below. In this infusible treatment step, oxidation causes intermolecular crosslinking of the materials constituting the crosslinked hollow fibers, improving the heat resistance of the hollow fibers. This effectively prevents the hollow fibers from melting in the carbonization treatment step described below. Furthermore, the infusible treatment not only improves the heat resistance of the crosslinked hollow fibers, but also allows for control of the strength characteristics and permeability of the hollow fiber carbon membrane finally obtained. After cooling the infusible hollow fibers, the hollow fibers are cut to a predetermined length, for example, 20 to 60 cm, to obtain units of 1,000 hollow fibers.

[0035] <Step (e)> Next, the infusible hollow fibers are carbonized. The carbonization is carried out by placing the cut hollow fibers in a container and heating them under a reduced pressure of preferably 10 Pa or less, more preferably 4 to 10 Pa, or under an inert gas atmosphere in which the air is replaced with helium gas, argon gas, nitrogen gas, or the like without reducing the pressure. This ultimately produces a hollow fiber carbon membrane. The carbonization conditions can be appropriately set depending on the material, type, and amount of the hollow fiber carbon membrane. Examples of suitable conditions include temperatures of 450 to 850°C, preferably 600 to 800°C, for 0.5 to 4 hours. This carbonization can increase the carbon content of the hollow fiber carbon membrane. The hollow fiber carbon membrane obtained after carbonization maintains its linear shape, making it highly moldable. For example, when packing the hollow fiber carbon membrane into a hollow fiber carbon membrane module, the packing density of the hollow fiber carbon membrane can be increased, resulting in the production of a hollow fiber carbon membrane module with high permeability.

[0036] [Hollow-fiber carbon membrane] The hollow-fiber carbon membrane produced by the above-described production method contains sulfur-crosslinked polyphenylene oxide, and therefore has a tensile strength of 30 MPa or more. Thus, the obtained hollow-fiber carbon membrane not only exhibits excellent separation properties equivalent to those of conventional hollow-fiber carbon membranes, but also exhibits superior tensile strength due to the large amount of sulfur crosslinked.

[0037] <Hollow-fiber carbon membrane for gas separation module> The hollow-fiber carbon membrane according to the present invention may be a hollow-fiber carbon membrane for gas separation module. Because such a hollow-fiber carbon membrane is produced by the hollow-fiber carbon membrane production method of the present invention, the hollow-fiber carbon membrane in the gas separation module is linear, which allows the packing density of the hollow-fiber carbon membrane in the module to be increased, thereby realizing a hollow-fiber carbon membrane for gas separation module with high permeation rate.

[0038] Examples of the present invention will be described below, but the present invention is not limited to these examples as long as they do not deviate from the spirit of the present invention. Furthermore, unless otherwise specified, room temperature is assumed to be within the range of 20°C ± 5°C.

[0039] Example 1 A carbon membrane forming solution was prepared, consisting of 28 parts by mass of polyphenylene oxide resin, 2.8 parts by mass of sulfur (10% by mass relative to the polyphenylene oxide resin), and 69.2 parts by mass of dimethylacetamide. The prepared membrane forming solution was heated to 130°C, and extruded into a water coagulation bath using a spinning nozzle with a double ring structure and ethylene glycol as a core liquid, followed by dry-wet spinning at a spinning speed of 15 m / min. The spun hollow fiber was wound around a cylindrical bobbin with a circumference of 90 cm. The wound hollow fiber was washed by submerging the cylindrical bobbin in water for half a day.

[0040] Next, hollow fibers were wound using the rectangular bobbin shown in Figure 2. The rectangular bobbin used was an aluminum bobbin with a rectangular cross section perpendicular to the rotation axis, dimensions of 120 cm in height, 80 cm in width, and 60 cm in depth, and a circumferential length per rotation of 360 cm. While rotating the rectangular bobbin and feeding the hollow fibers from the cylindrical bobbin, winding (hollow fiber feeding) was performed at a speed of 18 m / min with a hollow fiber spacing of 2 mm. The total number of winding rotations was 300, and the total length of the hollow fibers was approximately 1 km. The time required for this winding was approximately 1 hour.

[0041] Thereafter, crosslinking and infusibilization treatments were carried out as the first heating step. First, the rectangular bobbin around which the hollow fiber was wound was placed in a heating device with an internal volume of 150 cm in height, 100 cm in width, and 70 cm in depth. For the crosslinking treatment, the bobbin was heated to 200°C over approximately 1 hour, and then further heated to 220°C at a rate of 0.5°C / min. Subsequently, the crosslinking reaction was carried out by holding the bobbin at 220°C for 2 hours. For the subsequent infusibilization treatment, the bobbin was further heated from 220°C at a rate of 1°C / min to 280°C. The bobbin was held at 280°C for 2 hours, and then naturally cooled to room temperature.

[0042] After natural cooling, the hollow fibers were held on the bobbin without contact between the hollow fibers, just as they were during winding. Furthermore, the hollow fibers were not broken or crushed, and the moldability of the hollow fibers was good. Furthermore, by increasing the sulfur concentration to 10% by mass relative to the polyphenylene oxide resin, good hollow fibers could be molded without contact between the hollow fibers and without breakage or crushing. This demonstrates that the method of the present invention can mold good hollow fibers without using a resin tube, thereby reducing the cost of materials associated with using a resin tube.

[0043] After the first heating step, the straight hollow fibers were cut into 30 cm pieces using scissors to obtain approximately 3,600 hollow fibers. The cut hollow fibers were placed in a quartz glass tube and subjected to a second heating step, in which they were carbonized at 800°C for 1 hour in a nitrogen gas flow atmosphere, to produce approximately 3,600 hollow fiber carbon membranes.

[0044] The following gas permeation test was carried out on the prepared hollow fiber carbon membrane. The results are shown in Table 1. As shown in Table 1, it was revealed that the obtained hollow fiber carbon membrane had high separation performance (separation factor α) similar to that of conventional hollow fiber carbon membranes.

[0045] <Gas permeation test> One end of the hollow fiber carbon membrane was sealed with epoxy resin, and the other end was inserted 10 mm into the piping of a Swagelok metal gasket gland (6LV-4-VCR-3S-6MTB7). The gap between the hollow fiber carbon membrane and the gland piping up to 5 mm from the insertion point was glued with epoxy resin to produce a mini-module for gas separation evaluation. Several gases were pressurized to the outside of the hollow fiber carbon membrane at 200 kPa (gauge pressure), and the gas flow rate permeating to the tubing side was measured. The measured gas flow rate was divided by the membrane area, time, and pressure to calculate the gas permeation rate.

[0046]

[0047] <Strength characteristics> Both ends of the hollow fiber carbon membrane were fixed to the chucks of a tensile testing device (EZ-Test / CE manufactured by Shimadzu Corporation), and the effective length was set to 50 mm. A tensile stress was applied to the hollow fiber carbon membrane at a rate of 10 mm / min to measure the tensile strength. The resulting tensile strength was 35 MPa.

[0048] Comparative Example 1 The first heating step was carried out in the same manner as in Example 1, except that a carbon membrane forming solution containing 28 parts by mass of polyphenylene oxide resin, 0.8 parts by mass of sulfur (approximately 3% by mass relative to the polyphenylene oxide resin), and 71.2 parts by mass of dimethylacetamide was used, followed by natural cooling to room temperature. After natural cooling, the hollow fibers wound around the rectangular bobbin were observed. Numerous adhesions between the hollow fibers, breakages due to gravitational tension, and crushing were observed, which were likely due to insufficient crosslinking. Therefore, even when the first heating step was carried out under conditions in which the sulfur content in the carbon membrane forming solution was low, good hollow fibers could not be formed.

[0049] Furthermore, as a strength property, the tensile strength was measured for a portion of the hollow fiber that was not broken or crushed under the same measurement conditions as in Example 1, and the obtained tensile strength was 12 MPa. Comparison of the tensile strengths between Example 1 and Comparative Example 1 revealed that the strength properties of the hollow fiber carbon membrane can be improved by increasing the sulfur composition contained in the carbon membrane-forming dope solution and enhancing the crosslinkability.

[0050] Comparative Example 2: A carbon membrane forming solution containing 28 parts by mass of polyphenylene oxide resin, 2.8 parts by mass of sulfur (10% by mass relative to the polyphenylene oxide resin), and 69.2 parts by mass of dimethylacetamide was prepared under the same conditions as in Example 1, and dry / wet spinning and water washing were performed. Next, the obtained hollow fibers were cut into 30 cm lengths as samples, and each hollow fiber was inserted into a perfluoroalkoxyalkane resin tube based on the method described in the examples of WO 2016 / 093357. The insertion of 3,600 hollow fibers took approximately 6 hours.

[0051] Thus, when the first heating step was performed using a resin tube without using a square bobbin, the time required to insert 3,600 hollow fibers into the resin tube was 6 hours, whereas when winding using the square bobbin in this example, which corresponds to inserting hollow fibers into the resin tube, took only 1 hour, as described above. This demonstrates that by performing the winding work around the square bobbin as in this example, instead of the conventional manual work of inserting resin tubes, which requires careful handling, the manufacturing time and production costs can be reduced compared to inserting hollow fibers into the resin tube.

[0052] 1 hollow fiber 2 bobbin 3 corner portion 4 outer periphery

Claims

1. A method for producing a hollow fiber carbon membrane, comprising: (a) a step of preparing a carbon membrane dope solution, and forming a hollow fiber from the carbon membrane dope solution using a double annular nozzle by a spinning method using a non-solvent-induced separation method; (b) a step of winding the formed hollow fiber around a bobbin having a polygonal outer periphery; (c) a step of heating the wound hollow fiber in air at 200°C to 220°C while rotating the bobbin to perform a crosslinking treatment; (d) a step of heating the crosslinked hollow fiber from 200°C to 220°C and then to 250°C to perform an infusibilization treatment; and (e) a step of carbonizing the infusibilized hollow fiber, wherein the carbon membrane dope solution contains polyphenylene oxide in an amount to give a concentration of 15 to 40% by mass, sulfur in an amount to give a ratio of 7 to 15% by mass relative to the polyphenylene oxide, and a solvent capable of dissolving them.

2. The method for producing a hollow fiber carbon membrane according to claim 1, wherein the polygon is a quadrangle.

3. The method for producing a hollow fiber carbon membrane according to claim 1 or 2, wherein in step (b), the hollow fiber is wound up in a linear shape.

4. A hollow fiber carbon membrane containing sulfur-crosslinked polyphenylene oxide and having a tensile strength of 30 MPa or more.

5. The hollow fiber carbon membrane according to claim 4, which is a hollow fiber carbon membrane for a gas separation module.

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